It is known (see e.g. German Offenlegungsschrift No. 1,768,808) that 1,3,4-dioxazolinone-2 which is substituted by alkyl or aryl groups in the 5-position may be decomposed into isocyanates and carbon dioxide by heating to temperatures of from about 100.degree.C to about 200.degree.C in inert solvents. However, if attempts are made to decompose 5-vinyl- or 5-isopropenyl-1,3,4-dioxazolinone-2 into vinyl isocyanate or isopropenylisocyanate and carbon dioxide by the action of heat under the conditions previously known, secondary reactions (in particular, polymerization) occur. Accordingly, isocyanate-containing monomers cannot therefore be prepared in this way.
The unsaturated isocyanates are monomers which may be used in a variety of ways for the production of modified synthetic resins, [Chem. High Polymers Tokyo, 13, 125 (1956); Bull. Soc. Chim. Belge 65, 571 (1956); ibid 66, 229 (1957); Makromol. Chem. 47, 143 (1961), Makromol. Chem. 31, 230 (1959)]. The synthesis previously known, [see e.g. Journal of Organic Chemistry 26, 770-9 (1961), ibid 27, 1454-5 (1962); Chemische Berichte 98, 650-2 (1965)] are not suitable for commercial production since synthesis by way of the corresponding acid azides proceeds by way of dangerous explosive intermediates and requires expensive starting materials, such as methacrylic acid chloride and sodium azide. The problem therefore arises of finding some way of decomposing 5-isopropenyl-1,3,4-dioxazolinone-2 (which as is known may be prepared by a technically satisfactory process from very easily available starting materials, namely methacrylic acid esters, hydroxylamine and phosgene) into the desired isopropenyl isocyanate.